1. Field of the Invention
This invention relates to a process for the formation of a leafing type aluminum flake-containing metallic multi-layer coating film.
2. Description of Related Art
There has already been known a technique to form, on a substrate such as an automobile body panel, a multi-layer coating film, by applying an aluminum flake pigment-containing metallic coating on said substrate, and then applying, on the resultant coated surface, a clear coating which is capable of forming a transparent film.
The aluminum flake pigment to be compounded in a metallic coating is classified into a leafing type and a non-leafing type. In a metallic coating film which contains a leafing type aluminum flake pigment, the aluminum flake pigment floats up to the surface of said coating film (which phenomenon is called leafing) to form a continuous and dense aluminum plane which is oriented substantially parallel to the coated surface, resulting in the achievement of special effects such as a chrome plating-like finish, glittering brightness and strong flip-flop properties.
This metallic coating film per se is, however, inferior in chemical resistance such as acid resistance since aluminum flake pigment floats up to the surface of said coating film. In order to overcome this defect, the coated surface of said metallic coating film is usually coated with a clear coating. However, when a clear coating is applied onto the coated surface of a metallic coating film while the metallic coating is uncured, the orientation of leafing type aluminum flake is disturbed, resulting in the deterioration of a chrome plating-like finish (which phenomenon is called mottling). On the other hand, when a clear coating is applied after the metallic coating film is heat-cured, the interlayer adhesivity between the metallic coating film and the clear coating film is caused to be insufficient. Hence, it has been impossible to fully produce the above-mentioned various advantageous effects of a leafing type aluminum flake-containing metallic coating film.
As for a non-leafing type aluminum flake, it is uniformly dispersed in the whole of a coating film without causing leafing. Hence, when a clear coating is applied onto the surface of a metallic coating, there occurs neither mottling nor the reduction in interlayer adhesivity. However, the brightness and flip-flop effects of the film are weak, and, moreover, it is difficult to achieve a metallic coating film having a chrome plating-like finish.
In view of the above situation, the inventors of this invention studied how to improve the interlayer adhesivity between a metallic coating film and an adjacent film, without causing reduction in the above-mentioned special effects (e.g., dense metallic appearance of the coated surface, a chrome plating-like finish, strong brightness and flip-flop effects) possessed by a leafing type aluminum flake pigment-containing metallic coating film.